Code division multiple access (CDMA), and particularly direct sequence CDMA, is a technique for spread-spectrum digital communications used for many applications, including, for example, mobile communications. In direct sequence CDMA, data signals are combined with a spreading waveform in the form of a pseudo-random-noise code to form a coded signal for transmission. The code has a frequency (i.e., the chip rate) which may be a multiple of the frequency (i.e., the bit-rate or symbol-rate) of the data signal, so that an effect of combining the data signal and the spreading waveform is that the bit period is divided into smaller chip periods. At the receiver, the signal is combined with the same spreading code to extract the data signal. The technique provides high data capacity by spreading signal energy over a wide bandwidth to increase bandwidth utilization and reduce the effects of narrow-band interference. In direct sequence CDMA, the spreading code of the transmitter and receiver should be synchronized within as little as one chip period to achieve reliable communication. Multipath effects make synchronization more difficult since the wireless channel from a base station to a reception device may have several paths of different channel characteristics which may vary due to the movement of the reception device.
In some CDMA systems, such as a wideband CDMA (WCDMA) system and a WCDMA third generation partnership project (3GPP) system, a closed loop diversity mode may be implemented in which a base station uses two or more antennas to transmit to a mobile receiver. To improve reception of the CDMA signals, a feedback mechanism has been employed by the mobile receiver. The receiver may send the transmitter feedback bits to indicate to the transmitter to adjust or change the phase and/or amplitude components of the diversity mode signals. This feedback mechanism allows the transmitter to select weights suited to the condition and propagation characteristics of the channel between the base station and the mobile receiver. This also allows the mobile receiver to utilize the known weights in combining the multipath components of the received signal. In this way received power can be maximized. One problem, however, is that the feedback channel is not always reliable so that the weights used by the base station may be different than what the mobile receiver is expecting. This mismatch between weighs results in a reduction in performance. Unfortunately, there is no way for the mobile receiver to know when the transmitter does not receive the feedback information.
Thus there is a need for an improved receiver and method for weight detection. There is also a need for a receiver and method for weight detection suitable for use in closed loop diversity mode communication systems, including WCDMA systems.